1. Onosmodium molle Michx. (western false gromwell)

O. bejariense A. DC.

Map 1307, Pl. 310 c–j

Plants perennial herbs, with a stout, woody rootstock. Stems 30–120 cm long, erect or ascending to somewhat arched, solitary or few, unbranched or few-branched below the inflorescence, nearly glabrous to densely hairy. Leaves alternate, sessile, the basal leaves present only in seedlings, the lowermost leaves reduced and usually withered or shed at flowering. Leaf blades 2–14 cm long, 10–40 mm wide, narrowly lanceolate to lanceolate, elliptic, or ovate, angled or tapered at the base, angled or tapered to a sharply pointed tip, the upper surface densely pubescent with appressed to spreading, stiff, pustular-based hairs, the undersurface moderately to densely pubescent with softer, sometimes nonpustular-based hairs, with 2–4 prominent pairs of lateral veins, these usually strongly impressed on the upper surface and strongly ridged on the undersurface. Inflorescences often paired, terminal, appearing as dense clusters at the start of flowering, then becoming elongated into scorpioid, spikelike racemes, the flowers with stalks 0.3–1.0 mm long at flowering, these elongating to 1.5–3.0 mm at fruiting, ascending, each flower subtended by a leaflike bract 10–35 mm long. Cleistogamous flowers not produced. Calyces actinomorphic, 5-lobed nearly to base, the lobes 3.5–9.0 mm long at flowering, elongating slightly at fruiting, linear to narrowly triangular or narrowly oblanceolate, densely hairy on both surfaces, persistent and ascending at fruiting. Corollas 7–16 mm long at full flowering (see discussion above), tubular with a small bulge in the throat, actinomorphic, white to cream-colored or greenish yellow, hairy on the outer surface, the tube 5–12 mm long, the throat lacking scalelike appendages, the lobes 2–4 mm long. Stamens inserted near the tip of the corolla tube, the filaments very short, the anthers lanceolate to slightly arrowhead-shaped, not or only slightly exserted from the corolla. Ovary deeply 4-lobed, the style elongate, strongly exserted from the corolla, persistent at fruiting, stigma capitate, shallowly 2-lobed. Fruits dividing into mostly 1 or 2 nutlets, these 2.5–5.0 mm long, ovoid to broadly ovoid, sometimes with a shallow ventral groove or an indistinct, blunt ventral ridge, white to ivory-colored or brownish-tinged, attached to the flat gynobase at the base, the attachment scar relatively large, the surface smooth or rarely minutely pitted, sometimes shiny. 2n=24, 28. May–August.

Scattered, mostly south of the Missouri River (eastern U.S. west to Montana and New Mexico; Canada). Glades, savannas, bottomland forests, mesic to dry upland forests, ledges and tops of bluffs, upland prairies, and loess hill prairies; also old fields, railroads, and roadsides; often on calcareous substrates.

Onosmodium molle is a widespread species that is polymorphic in size, branching, pubescence, and fruit characters. Correlation of the variation with geographic regions has led to the recognition of several taxa as varieties (Cronquist, 1959), subspecies (Cochrane, 1976; Turner, 1995), or species (Mackenzie, 1906; Steyermark, 1963; Turner, 1995) within the complex. Intermediates between the taxa are commonly encountered, and some characters used by previous authors to separate them, such as nutlet size, pitting, and luster, do not hold up under careful scrutiny (Cochrane, 1976). Most recently, Turner (1995) recognized the Missouri material as varieties of O. bejariense and restricted O. molle to cedar glades in Tennessee and adjacent states, but this treatment is not strongly supported. We follow the nomenclature of Cochrane (1976) and recognize the Missouri material as subspecies of O. molle. Subspecific status is supported by the correlation of variation with geographic distribution as mapped by Turner (1995). Two other subspecies do not occur in Missouri. Onosmodium molle ssp. molle appears to be restricted to Tennessee, Kentucky, northern Alabama, and southern Illinois (Baskin et al., 1983) and differs in its slightly narrower leaves with relatively soft, dense pubescence on both surfaces. The ssp. bejariense (A. DC.) Cochrane occupies the southwestern portion of the species range in portions of Texas, Oklahoma, Arkansas, and Louisiana and has somewhat longer (2–4 mm vs. 1.0–1.5 mm) stem hairs than does ssp. occidentale, as well as slightly smaller nutlets (Turner, 1995). The entire complex would benefit from more detailed biosystematic study.

In Missouri, a small number of specimens exist that are intermediate between all combinations of pairs of the three subspecies treated below. These specimens represent putative hybrids, but to date there is no experimental evidence to support this hypothesis. It also is not known whether such specimens were collected from mixed populations of the putative parental subspecies or whether these morphological intermediates form their own uniform populations. The plants in question appear to produce fully formed nutlets.